Glee's tribute episode to Cory Monteith will be missing one important player when it airs this week: Cory's former on-screen girlfriend Dianna Agron.

Glee's tribute episode to Cory Monteith will be missing one important player when it airs this week: Cory's former on-screen girlfriend Dianna Agron.

Dianna, who played Quinn, won't be back to farewell Cory's character Finn, and it's because Dianna is "intensely disliked" by her co-stars and the show's co-creator Ryan Murphy, according to a high-level source on the show.

"It's shocking, because even though she's not contracted for this season, many other actors returned to pay tribute to Cory … even ones with less of a story connection to Finn than Dianna had," the source told Radar Online.

"Remember, she played his GIRLFRIEND on the series, and was a major part of his storyline."

It does strike us as bizarre that she wouldn't be asked back even when other former Glee stars are returning for the emotional episode (see the trailer above).

The source added that Cory's on-and-off-screen lover Lea Michele isn't a fan of Dianna either. Lea and Ryan Murphy "intensely dislike Dianna and have both worked to marginalise her as much as possible", says the source. "They never saw her as a team player. They simply did not want her sharing the glory for this very special episode."

Dianna is yet to comment on the snub. The 27-year-old recently spoke of Cory's tragic death, caused by a lethal cocktail of heroin and champagne on July 13.

"It's one of those things that still doesn't seem real," Dianna told talk show host Katie Couric. "You just take out a new lease on life and you realise that he's smiling down on us."